Driving device and electronic apparatus using the same

ABSTRACT

A driving device includes a dimmer, a rectifying-filtering unit, a rectifying-dividing unit, a control unit, and a voltage transforming unit. The dimmer is used for receiving an alternating current (AC) voltage from a power supply, and generating a primary voltage for controlling the brightness of a luminous element. The rectifying-filtering unit is used for rectifying and filtering the primary voltage to generate a secondary voltage. The rectifying-dividing unit is used for rectifying and dividing the primary voltage to generate a detecting voltage. The control unit is used for receiving the secondary voltage, and generating a pulse voltage whose duty cycle is variable with the detecting voltage. The voltage transforming unit is used for transforming the secondary voltage to a driving voltage for driving the luminous element to emit light according to the pulse voltage. A related electronic apparatus is also provided.

BACKGROUND

1. Technical Field

The disclosed embodiments relate to electronic apparatus; andparticularly to driving devices for light emitting diodes (LEDs) used inthe electronic apparatus.

2. Description of Related Art

A triode for alternating current (TRIAC) is widely used in lightemitting diode (LED) driving circuits. The TRIAC has an on-state and anoff-state. A trigger unit is used for triggering the TRIAC to theon-state or the off-state. When the TRIAC is in the on-state, analternating current (AC) voltage, is provided to the LED drivingcircuit, so the LED driving circuit can drive a plurality of LEDs toemit light. When the TRIAC is in the off-state, the AC voltage is notprovided to the LED driving circuit, so the LEDs cannot emit light.

However, the frequency of changing from the on-state to the off-state orfrom the off-state to the on-state is often smaller than 50 Hz,therefore the flicker frequency of light emitted by the LEDs is alsosmaller than 50 Hz, and users may feel that the LED is flashing andunstable.

Therefore, there is room for improvement in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with referenceto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the present embodiments.Moreover, in the drawings, like reference numerals designatecorresponding parts throughout two views.

FIG. 1 is a block diagram of an electronic apparatus in accordance withan exemplary embodiment.

FIG. 2 is a circuit diagram of the electronic apparatus of FIG. 1 inaccordance with the exemplary embodiment.

DETAILED DESCRIPTION

Referring to FIG. 1, an electronic apparatus 900 includes a drivingdevice 100 and a luminous element 200. The driving device 100 is usedfor receiving an alternating current (AC) voltage from a power supply300, and generating a driving voltage to drive the luminous element 200to emit light. The driving device 100 includes a dimmer 12, arectifying-filtering unit 14, a rectifying-dividing unit 16, a controlunit 20, and a voltage transforming unit 24.

The dimmer 12 is used for receiving the AC voltage, and generating aprimary voltage for controlling the brightness of the luminous element200. In detail, see FIG. 2, the dimmer 12 includes a triode foralternating current (TRIAC) 120 and a trigger unit 124. The TRIAC 120includes a base terminal, a first main terminal, and a second mainterminal. The base terminal is connected to the trigger unit 124, suchas a diode for alternating current (DIAC); the first main terminal isconnected to the power supply 300; the second main terminal is connectedto the rectifying-filtering unit 14 and the rectifying-dividing unit 16.The TRIAC 120 has an off-state and an on-state. The trigger unit 124 isused for triggering the TRIAC 120 to the off-state or the on-state. Whenthe TRIAC 120 is in the on-state, the AC voltage is respectivelyprovided to the rectifying-filtering unit 14 and the rectifying-dividingunit 16. When the TRIAC 120 is in the off-state, the AC voltage is notprovided to the rectifying-filtering unit 14 and the rectifying-dividingunit 16.

The rectifying-filtering unit 14 is used for rectifying and filteringthe primary voltage to generate a secondary voltage.

The rectifying-dividing unit 16 is used for rectifying and dividing theprimary voltage to generate a detecting voltage.

The control unit 20 is coupled to the rectifying-filtering unit 14, therectifying-dividing unit 16, and the voltage transforming unit 24. Thecontrol unit 20 is used for receiving the secondary voltage and thedetecting voltage, and generating a pulse voltage whose duty cycle isvaried with the detecting voltage.

The voltage transforming unit 24 is used for transforming the secondaryvoltage to the driving voltage according to the pulse voltage. Thedriving voltage is provided to the luminous element 200 and is used fordriving the luminous element 200 to emit light.

Referring to FIG. 2, the luminous element 200 includes a plurality ofLEDs connected in series. The rectifying-dividing unit 16 includes afirst diode D1, a second diode D2, a first resistor R1, and a secondresistor R2. An anode of the first diode D1 is connected to the secondmain terminal of the TRIAC 120, a cathode of the first diode D1 isconnected to a cathode of the second diode D2, and an anode of thesecond diode D2 is grounded. One end of the first resistor R1 isconnected between the cathode of the first diode D1 and the cathode ofthe second diode D2, the other end of the first resistor R1 is groundedthrough the second resistor R2.

The control unit 20 includes a terminal connected between the firstresistor R1 and the second resistor R2. The control unit 20 includes areference voltage unit 202, a first comparison unit A1, a secondcomparison unit A2, a switch 204, and a pulse width modulation (PWM)unit 205. The switch 204 is connected between the second comparison unitA2 and the PWM unit 205. The reference voltage unit 202 is used forproviding a first reference voltage V_(Ref1) and a second referencevoltage V_(Ref2). The first comparison unit A1 is used for comparing thedetecting voltage with the first reference voltage V_(Ref1), generatinga first level signal if the detecting voltage is larger than the firstreference voltage V_(Ref1), and generating a second level signal if thedetecting voltage is smaller than the first reference voltage V_(Ref1).In this embodiment, the first level signal is a high level signal, andthe second level signal is a low level signal.

The second comparison unit A2 is used for comparing the detectingvoltage with the second reference voltage V_(Ref2), generating a controlvoltage if the detecting voltage is smaller than the second referencevoltage V_(Ref2), and outputting the detecting voltage if the detectingvoltage is larger than the second reference voltage V_(Ref2). Thecontrol voltage linearly increases with the detecting voltage. Theswitch 204 is turned on according to the first level signal andestablishes an electrical connection between the second comparison unitA2 and the PWM unit 205. The switch 204 cuts off the electricalconnection between the second comparison unit A2 and the PWM unit 205according to the second level signal. The PWM unit 205 is used forreceiving the secondary voltage to be powered on, generating the pulsevoltage whose duty cycle is linearly increased with the control voltagewhen received the control voltage, and generating the pulse voltagewhose duty cycle is invariable when received the detecting voltage.

In this embodiment, both of the first comparison unit A1 and the secondcomparison unit A2 are an operational amplifier. The first operationalamplifier A1 includes a first non-inverting input terminal 30, a firstinverting input terminal 32, and a first output terminal 34. The secondoperational amplifier A2 includes a second non-inverting input terminal40, a third non-inverting input terminal 42, a second inverting inputterminal 44, and a second output terminal 45. The first non-invertinginput terminal 30 is connected to the second inverting input terminal44. The first inverting input terminal 32 is used for receiving thefirst reference voltage V_(Ref1). The first non-inverting input terminal30 and the second inverting input terminal 44 are connected between thefirst resistor R1 and the second resistor R2. The second non-invertinginput terminal 40 is connected to the second output terminal 45, and thethird non-inverting input terminal 42 is used for receiving the secondreference voltage V_(Ref2). The switch 204 is connected between thesecond output terminal 45 and the PWM unit 205, the first outputterminal 34 is used for outputting a control signal to turn on/off theswitch 204. The PWM unit 205 includes a control terminal 215, a firstterminal 225, and a second terminal 245. The control terminal 215 isconnected to the second output terminal 45 through the switch 204. Thefirst terminal 225 is connected to the rectifying-filtering unit 14. Thesecond terminal 245 is connected to the voltage transforming unit 24.

The voltage transforming unit 24 is used for transforming the secondaryvoltage to the driving voltage when receiving the pulse voltage whoseduty cycle is invariable, and the driving voltage is invariable.Therefore, the brightness of the luminous element 200 is stable.

The voltage transforming unit 24 is used for transforming the secondaryvoltage to the driving voltage when receiving the pulse voltage whoseduty cycle is linearly increased with the control voltage, and thedriving voltage is also linearly increased. Therefore, brightness of theluminous element 200 is increased. Because frequency of the PWM unit 205is 20 KHz˜100 KHz, therefore frequency of the pulse voltage generated bythe PWM unit 205 is much higher than 50 Hz, the flicker frequency oflight emitted by the luminous element 200 is also higher than 50 Hz, andthe luminous element 200 appears stable.

Further alternative embodiments will become apparent to those skilled inthe art without departing from the spirit and scope of what is claimed.Accordingly, the present invention should be deemed not to be limited tothe above detailed description, but rather only by the claims thatfollow and equivalents thereof.

What is claimed is:
 1. A driving device used for receiving analternating current (AC) voltage from a power supply, and generating adriving voltage to drive a luminous element to emit light, the drivingdevice comprising: a dimmer for receiving the AC voltage, and generatinga primary voltage for controlling the brightness of the luminouselement; a rectifying-filtering unit for rectifying and filtering theprimary voltage to generate a secondary voltage; a rectifying-dividingunit for rectifying and dividing the primary voltage to generate adetecting voltage; a control unit for receiving the secondary voltage,and generating a pulse voltage whose duty cycle is variable with thedetecting voltage; and a voltage transforming unit for transforming thesecondary voltage to the driving voltage according to the pulse voltage.2. The driving device of claim 1, wherein the control unit comprises areference voltage unit for providing a first reference voltage and asecond reference voltage, a first comparison unit, a second comparisonunit, a pulse width modulation (PWM) unit, and a switch connectedbetween the second comparison unit and the PWM unit, the firstcomparison unit is used for comparing the detecting voltage with thefirst reference voltage, and generating a first level signal if thedetecting voltage is larger than the first reference voltage, the secondcomparison unit is used for comparing the detecting voltage with thesecond reference voltage, and generating a control voltage linearlyincreasing with the detecting voltage if the detecting voltage issmaller than the second reference voltage, the switch is turned onaccording to the first level signal and establishes an electricalconnection between the second comparison unit and the PWM unit, the PWMunit is used for receiving the secondary voltage to be powered on, andgenerating the pulse voltage whose duty cycle is linearly increased withthe control voltage when receiving the control voltage.
 3. The drivingdevice of claim 2, wherein the second comparison unit outputs thedetecting voltage if the detecting voltage is larger than the secondreference voltage, the PWM unit generates the pulse voltage whose dutycycle is invariable when receiving the detecting voltage.
 4. The drivingdevice of claim 2, wherein the first comparison unit generates a secondlevel signal if the detecting voltage is smaller than the firstreference voltage, the switch cuts off the electrical connection betweenthe second comparison unit and the PWM unit according to the secondlevel signal.
 5. The driving device of claim 2, wherein the firstcomparison unit is a first operational amplifier, the second comparisonunit is a second operational amplifier, the first operational amplifiercomprises a first non-inverting input terminal, a first inverting inputterminal, and a first output terminal, the second operational amplifiercomprises a second non-inverting input terminal, a third non-invertinginput terminal, a second inverting input terminal, and a second outputterminal, the first non-inverting input terminal is connected to thesecond inverting input terminal, the first inverting input terminal isused for receiving the first reference voltage, the first non-invertinginput terminal and the second inverting input terminal are connectedbetween the first resistor and the second resistor, the secondnon-inverting input terminal is connected to the second output terminal,the third non-inverting input terminal is used for receiving the secondreference voltage, the switch is connected between the second outputterminal and the PWM unit, the first output terminal is used foroutputting a control signal to turn on/off the switch, the PWM unitcomprises a control terminal, a first terminal, and a second terminal,the control terminal is connected to the second output terminal throughthe switch, the first terminal is connected to the rectifying-filteringunit, the second terminal is connected to the voltage transforming unit.6. The driving device of claim 2, wherein the first reference voltage issmaller than the second reference voltage.
 7. The driving device ofclaim 1, wherein the dimmer comprises a triode for alternating current(TRIAC) and a trigger unit, the TRIAC have an off-state and an on-state,the trigger unit is used for triggering the TRIAC to the off-state orthe on-state, when the TRIAC is in the on-state, the AC voltage isprovided to the rectifying-filtering unit and the rectifying-dividingunit respectively, when the TRIAC is in the off-state, the AC voltage isnot provided to the rectifying-filtering unit and therectifying-dividing unit.
 8. The driving device of claim 7, wherein theTRIAC comprises a base terminal, a first main terminal, and a secondmain terminal, the base terminal is connected to the trigger unit, thefirst main terminal is connected to the power supply, the second mainterminal is connected to the rectifying-filtering unit and therectifying-dividing unit.
 9. The driving device of claim 1, wherein therectifying-dividing unit comprises a first diode, a second diode, afirst resistor, and a second resistor, an anode of the first diode isconnected to the dimmer, a cathode of the first diode is connected to acathode of the second diode, an anode of the second diode is grounded,one end of the first resistor is connected between the cathode of thefirst diode and the cathode of the second diode, the other end of thefirst resistor is grounded through the second resistor, the control unitcomprises a terminal connected between the first resistor and the secondresistor.
 10. A driving device used for receiving an alternating current(AC) voltage from a power supply, and generating a driving voltage todrive a luminous element to emit light, the driving device comprising: adimmer for receiving the AC voltage, and generating a primary voltagefor controlling the brightness of the luminous element; arectifying-filtering unit for rectifying and filtering the primaryvoltage to generate a secondary voltage; a rectifying-dividing unit forrectifying and dividing the primary voltage to generate a detectingvoltage; a control unit for comparing the detecting voltage with a firstreference voltage and a second reference voltage, and generating a pulsevoltage whose duty cycle is variable if the detecting voltage is largerthan a first reference voltage and smaller than a second referencevoltage; and a voltage transforming unit for transforming the secondaryvoltage to the driving voltage according to the pulse voltage.
 11. Thedriving device of claim 10, wherein control unit for generating thepulse voltage whose duty cycle is invariable if the detecting voltage islarger than the second reference voltage, and the driving voltage isinvariable.
 12. The driving device of claim 10, wherein the control unitcomprises a reference voltage unit for providing the first referencevoltage and the second reference voltage, a first comparison unit, asecond comparison unit, a pulse width modulation (PWM) unit, and aswitch connected between the second comparison unit and the PWM unit,the first comparison unit is used for comparing the detecting voltagewith the first reference voltage, and generating a first level signal ifthe detecting voltage is larger than the first reference voltage, thesecond comparison unit is used for comparing the detecting voltage withthe second reference voltage, and generating a control voltage linearlyincreasing with the detecting voltage if the detecting voltage issmaller than the second reference voltage, the switch is turned onaccording to the first level signal and establishes an electricalconnection between the second comparison unit and the PWM unit, the PWMunit is used for receiving the secondary voltage to be powered on, andgenerating the pulse voltage whose duty cycle is linearly increased withthe control voltage when receiving the control voltage.
 13. The drivingdevice of claim 12, wherein the second comparison unit outputs thedetecting voltage if the detecting voltage is larger than the secondreference voltage, the PWM unit generates the pulse voltage whose dutycycle is invariable when receiving the detecting voltage.
 14. Thedriving device of claim 12, wherein the first comparison unit generatesa second level signal if the detecting voltage is smaller than the firstreference voltage, the switch cuts off the electrical connection betweenthe second comparison unit and the PWM unit according to the secondlevel signal.
 15. The driving device of claim 12, wherein the firstcomparison unit is a first operational amplifier, the second comparisonunit is a second operational amplifier, the first operational amplifiercomprises a first non-inverting input terminal, a first inverting inputterminal, and a first output terminal, the second operational amplifiercomprises a second non-inverting input terminal, a third non-invertinginput terminal, a second inverting input terminal, and a second outputterminal, the first non-inverting input terminal is connected to thesecond inverting input terminal, the first inverting input terminal isused for receiving the first reference voltage, the first non-invertinginput terminal and the second inverting input terminal are connectedbetween the first resistor and the second resistor, the secondnon-inverting input terminal is connected to the second output terminal,the third non-inverting input terminal is used for receiving the secondreference voltage, the switch is connected between the second outputterminal and the PWM unit, the first output terminal is used foroutputting a control signal to turn on/off the switch, the PWM unitcomprises a control terminal, a first terminal, and a second terminal,the control terminal is connected to the second output terminal throughthe switch, the first terminal is connected to the rectifying-filteringunit, the second terminal is connected to the voltage transforming unit.16. An electronic apparatus comprising: a luminous element; and andriving device for receiving an alternating current (AC) voltage from apower supply and generating a driving voltage to drive the luminouselement to emit light, the driving device comprising: a dimmer forreceiving the AC voltage, and generating a primary voltage forcontrolling the brightness of the luminous element; arectifying-filtering unit for rectifying and filtering the primaryvoltage to generate a secondary voltage; a rectifying-dividing unit forrectifying and dividing the primary voltage to generate a detectingvoltage; a control unit for receiving the secondary voltage, andgenerating a pulse voltage whose duty cycle is variable with thedetecting voltage; and a voltage transforming unit for transforming thesecondary voltage to the driving voltage according to the pulse voltage.17. The electronic apparatus of claim 16, wherein the control unitcomprises a reference voltage unit for providing a first referencevoltage and a second reference voltage, a first comparison unit, asecond comparison unit, a pulse width modulation (PWM) unit, and aswitch connected between the second comparison unit and the PWM unit,the first comparison unit is used for comparing the detecting voltagewith the first reference voltage, and generating a first level signal ifthe detecting voltage is larger than the first reference voltage, thesecond comparison unit is used for comparing the detecting voltage withthe second reference voltage, and generating a control voltage linearlyincreasing with the detecting voltage if the detecting voltage issmaller than the second reference voltage, the switch is turned onaccording to the first level signal and establishes an electricalconnection between the second comparison unit and the PWM unit, the PWMunit is used for receiving the secondary voltage to be powered on, andgenerating the pulse voltage whose duty cycle is linearly increased withthe control voltage when receiving the control voltage.
 18. Theelectronic apparatus of claim 17, wherein the second comparison unitoutputs the detecting voltage if the detecting voltage is larger thanthe second reference voltage, the PWM unit generates the pulse voltagewhose duty cycle is invariable when receiving the detecting voltage. 19.The electronic apparatus of claim 17, wherein the first comparison unitgenerates a second level signal if the detecting voltage is smaller thanthe first reference voltage, the switch cuts off the electricalconnection between the second comparison unit and the PWM unit accordingto the second level signal.
 20. The electronic apparatus of claim 17,wherein the first comparison unit is a first operational amplifier, thesecond comparison unit is a second operational amplifier, the firstoperational amplifier comprises a first non-inverting input terminal, afirst inverting input terminal, and a first output terminal, the secondoperational amplifier comprises a second non-inverting input terminal, athird non-inverting input terminal, a second inverting input terminal,and a second output terminal, the first non-inverting input terminal isconnected to the second inverting input terminal, the first invertinginput terminal is used for receiving the first reference voltage, thefirst non-inverting input terminal and the second inverting inputterminal are connected between the first resistor and the secondresistor, the second non-inverting input terminal is connected to thesecond output terminal, the third non-inverting input terminal is usedfor receiving the second reference voltage, the switch is connectedbetween the second output terminal and the PWM unit, the first outputterminal is used for outputting a control signal to turn on/off theswitch, the PWM unit comprises a control terminal, a first terminal, anda second terminal, the control terminal is connected to the secondoutput terminal through the switch, the first terminal is connected tothe rectifying-filtering unit, the second terminal is connected to thevoltage transforming unit.